When a group of researchers first started this long-term study 20 years ago in rural North Carolina, they didn’t expect to be presented with a sociological godsend. The original goal was simple: to observe the mental condition, performance, and health of 1,420 low-income children.

The study ended up with vastly more interesting data than they expected because approximately 4 years into The Great Smoky Mountains Study of Youth about 25% of their test group saw their average family income increase significantly. These children and their families were members of the Eastern Band of Cherokee Indians, which had just built a casino on the reservation. After that point, every tribal citizen earned a share in the profits, meaning approximately an extra $4,000 a year per capita.

As to be expected, this increase in funds helped the families and was enough to boost household income by 20% on average. The unexpected changes appeared on the psychological, sociological and economic levels, the sudden increase of family income within their test group offered a rare glimpse into the subtle but important ways in which money can alter a child’s life. The dataset is so rich that scientists continue to study and reference it to this day.

“It would be almost impossible to replicate this kind of longitudinal study,” said Randall Akee, a professor at the University of California, Los Angeles “Especially for a sample this large. This is the sort of circumstance you dream of as a researcher.”

Randall Akee, along with other researchers, recently revisited the data to analyze each child’s personality and behavior both in the years before the casino was built and in those after.

As part of the original study, the children and parents were asked a series of questions, designed to measure, among other things, a number of personality traits. The same questions were posed every other year for 10 years. Akee’s goal was to notice any significant changes—positive or negative—resulting from the extra household income. Their findings, published by the National Bureau of Economic Research last month, are another indication that a guarenteed “basic income” may be cheaper for society than our current system.

“This was hugely important to the development of the children, to their wellbeing” said Akee. “And the effect wasn’t small either—it was actually fairly large.”

Not only did the extra money lower the prevalence of behavioral and emotional disorders among the children, but it also boosted two key personality traits that are often seen to go hand in hand with long-term positive life outcomes.

The first factor is conscientiousness, which is low in those tend to lie, to break rules, and to have trouble paying attention. The second factor is agreeableness, which leads to greater comfort around people, tolerance for differences, and aptness for teamwork.

The researchers also observed a slight uptick in neuroticism, which, they explained, is a good sign. Neuroticism is generally considered to be a positive trait allowing greater reflection and even creativity, so long as one does not have too much of it.

“We’re talking about all sorts of good, positive, long-term things,” said Emilia Simeonova, a professor at Johns Hopkins University who studies the economics of health, and one of the paper’s co-authors. “There are very powerful correlations between conscientiousness and agreeableness and the ability to hold a job, to maintain a steady relationship. The two allow for people to succeed socially and professionally.”

Remarkably, the most radical change was seen in the children who were previously the most deficient. “This actually reduces inequality with respect to personality traits,” said Akee. “On average, everyone is benefiting, but in particular it’s helping the people who need it the most.”

Why exactly this happened is something neither Akee nor any of his co-researchers can say with even paramount certainty: after all, correlation and causation are not equivalent. There are a few ideas flying around the professional world, and they know, based on the interviews with parents, that the relationship between spouses tended to improve as a result. They also know that the relationship between the parents and their children tended to improve, and they know that the parents tended to drink less alcohol.

“There is a lot of literature that shows in order to change outcomes among children you are best off treating the parents first,” said Simeonova. “And these are really clear changes in the parents.”

There’s also the question of stress, which the extra money helps relieve—even if only a little. While the added income wasn’t enough to allow parents to quit their jobs, it’s a base level that helped with rent and food and other basic expenses that removes some of the day-to-day survival stress.

“We know that the thing poor couples fight about the most is money,” he said. “Off the bat, this means a more harmonious family environment.”

For the most part, scientists agree that the window for improvement in a child’s cognitive abilities is short-lived. By the age of about 8, children have set themselves on a path, Akee said. What comes next happens, more or less, is within the confines of the limits that were created in their early years.

One’s personality, on the other hand, is malleable well into adolescence. What’s more, the changes tend to be fairly permanent.

“All of the evidence points to the idea if they change in the teenage years, they will stay changed forever,” said Akee. “In this case, the kids will likely maintain a different level of conscientiousness and agreeableness for life.”

Experts have known about the power of intervention for some time. A lot of previous research has shown that educational interventions can have sizable impacts on personality traits and, in turn, life outcomes. But rarely, if ever before, have researchers been able to observe the impact of a change in income across such a large group and over such a period of time.

“We know that low income kids are worse off in a number of ways, in terms of cognitive abilities and behavioral disorders, than their counterparts in much more affluent areas,” said Simeonova. “Now we have a sense of what even just a little money can do change these things, to change their lives.”